The inheritance by an insect vector of the ability to transmit a plant virus

Abstract The leaf hopper, Cicadulina mbila Naude, is normally an efficient vector of the virus of streak disease of maize (Storey, 1925). I have, however, encountered exceptional individuals of this insect-species which were unable to transmit the virus (Storey, 1928). An attempt to discover the reason for their anomalous behaviour led me to undertake studies of the breeding of this species. The results so obtained, which show that the ability to transmit is an hereditary character, have been briefly reported (Storey, 1931), and I now present a full account of this work. Since these studies introduce a new conception into pathology, I find it necessary to give my definition of certain current terms and to utilise two new ones. I employ transmission in the restricted sense of the act of transfer of a virus by a vector from a diseased to a healthy plant in the natural processof that vector's feeding. I introduce the term activity to denote an insect’s inherent potentiality to transmit a virus ; inactivity to denote the absence of that inherent potentiality. An insect is viruliferous or non-viruliferous according as it is, or is not, actually carrying a virus in such a way that it inoculates that virus into a plant on which it feeds, and in consequence causes the plant to develop the symptoms of the disease.